Ski boots are already known whose upper, articulated on a bottom shell about a horizontal and transverse axis, comprises a front part or spoiler partially overlapping the bottom shell by its lower, front part. In a boot of this type, which is described in Patent Fr-A-2 590 129, the lower, front part of the spoiler comprises a transversely extending slot which forwardly defines an end part of the spoiler constituting a flexion piece. In this transverse slot is housed a slide tightly fitted between the two longitudinal edges of the slot and whose position is adjustable along the slot. This slide makes it possible to adjust, as desired, the control of the flexion of the articulated upper, depending on the position that the slide occupies in the slot.
In the ski boot described in the patent mentioned above, the slide is provided with at least one locking catch normally projecting laterally under the action of elastic return means in order to be able to engage in holes or notches provided in at least one of the edges of the slot in order to immobilize the slide in the desired position of adjustment. This catch, which is elastically urged towards its extended position, may be retracted inside the slide in order to allow displacement thereof, by action on a push element acting on a relatively complex connection mechanism.